CN109943772B - Steel material for graphite steel and graphite steel with improved machinability - Google Patents
Steel material for graphite steel and graphite steel with improved machinability Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
The invention discloses a steel material for graphite steel and graphite steel with improved machinability. A steel material for graphite steel according to one embodiment of the present invention includes, in wt%: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less (excluding 0), S: less than or equal to 0.030% (excluding 0), and the balance Fe and other unavoidable impurities.
Description
Technical Field
The present invention relates to a graphite steel having improved machinability. More particularly, the present invention relates to a steel material for graphite steel and graphite steel containing fine and uniform graphite and having improved machinability.
Background
In general, free-cutting steels containing free-cutting elements such as Pb, Bi, and S are used as materials for machine parts and the like that require machinability. The most typical free-cutting steel, i.e., free-cutting steel containing Pb, emits harmful substances such as toxic fumes (fume) during cutting operation, is very harmful to the human body, and has a problem of being very disadvantageous to the reuse of steel. Therefore, although it has been proposed to add S, Bi, Te, Sn, etc. in order to solve these problems, the steel material added with Bi has a problem that cracks are easily generated during production and thus it is very difficult to produce the steel material, and the steel material added with S, Te and Sn also has a problem that cracks are generated during hot rolling.
The steel proposed to solve the above problems is graphite steel. The graphite steel is a steel containing fine graphite particles in a ferrite matrix or a ferrite and pearlite matrix, and the fine graphite particles in the graphite steel serve as a crack breaker (source) during cutting, thereby having a property of good machinability.
However, despite these advantages, graphite steel is not yet popular. This is because, when carbon is added to steel, graphite precipitates as cementite as a metastable phase even though graphite is a stable phase, and if heat treatment is not performed for a long time of 10 hours or more, it is difficult to precipitate graphite, and decarburization occurs during such a long heat treatment, which adversely affects the properties of the final product.
Furthermore, even if graphite particles are precipitated by the graphitization heat treatment, if graphite is coarsely precipitated in the matrix of the steel, the possibility of crack generation becomes high, and if the graphite particles are not spherical but unevenly distributed in an irregular shape, the performance distribution at the time of cutting becomes uneven, so that the chip breaking property or the surface roughness becomes very poor, the tool life is shortened, and the advantage of the graphite steel is difficult to obtain.
Therefore, there is a need for a steel material for graphite steel that can significantly reduce the heat treatment time and can uniformly distribute fine graphite particles in a regular shape in a matrix during heat treatment, and graphite steel derived therefrom with improved machinability.
Disclosure of Invention
Technical problem
An object of the present invention is to provide a steel material for graphite steel, which can significantly shorten the heat treatment time and can uniformly distribute fine graphite particles in a regular shape in a matrix during heat treatment.
Another aspect of the present invention is to provide a graphite steel having excellent machinability.
Technical scheme
A steel material for graphite steel according to one embodiment of the present invention includes, in wt%: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less (excluding 0), S: less than or equal to 0.030% (excluding 0), and the balance Fe and other unavoidable impurities.
Further, according to an embodiment of the present invention, the steel material for graphite steel satisfies the following formula (1).
Formula (1): -0.01 ≤ Ti-3.43 × [ N ] 0.01 ≤
Wherein [ Ti ] and [ N ] each represent a weight% of the element.
Further, according to an embodiment of the present invention, the steel material for graphite steel satisfies the following formula (2).
Formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ] and [ Mn ] each represent the weight% of the element.
The graphite steel for improving machinability according to one embodiment of the present invention comprises, in wt.%, C: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less (excluding 0), S: 0.030% or less (excluding 0), and the balance being Fe and other unavoidable impurities, and 2.0% or more by area fraction of graphite particles contained in the ferrite matrix, and the graphite particles may have an average aspect ratio of 2.0 or less.
Wherein the aspect ratio of the graphite particles means the ratio of the longest axis to the shortest axis of one graphite particle.
Further, according to an embodiment of the present invention, the graphite steel for improving machinability satisfies the following formula (1).
Formula (1): -0.01 ≤ Ti-3.43 × [ N ] 0.01 ≤
Wherein [ Ti ] and [ N ] each represent a weight% of the element.
Further, according to an embodiment of the present invention, the graphite steel for improving machinability satisfies the following formula (2).
Formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ] and [ Mn ] each represent the weight% of the element.
Further, according to an embodiment of the present invention, the graphite particles may have an average particle size of 5 μm or less.
Further, according to an embodiment of the present invention, the number of the graphite particles per unit area may be 1000/mm2To 5000 pieces/mm2。
Further, according to an embodiment of the present invention, the graphite steel may have a hardness of 70HRB to 80 HRB.
Advantageous effects
The graphite steel of the present invention is excellent in machinability and therefore can be used as a material for machine parts of industrial machines, automobiles, and the like.
Detailed Description
A steel material for graphite steel according to one embodiment of the present invention includes, in wt%: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less (excluding 0), S: less than or equal to 0.030% (excluding 0), and the balance Fe and other unavoidable impurities.
The following embodiments are provided to fully convey the technical idea of the present invention to those skilled in the art to which the present invention pertains. The present invention is not limited to the following embodiments, and can be implemented in other ways. For the sake of clarity, parts not relevant to the description are omitted in the drawings, and the sizes of the constituent elements are slightly enlarged for easy understanding.
In the following description, when a certain component is "included" in a certain portion, unless specifically stated to the contrary, it means that other components may be included, and other components are not excluded.
The singular is also intended to include the plural unless the context otherwise indicates.
The following describes a steel material in which fine graphite particles are uniformly distributed in a regular shape in a matrix during graphitization heat treatment.
Embodiments according to the present invention are described in detail below with reference to the accompanying drawings. First, a steel material for graphite steel will be described, and then a graphite steel with improved machinability will be described.
A steel material for graphite steel according to one aspect of the present invention includes, in wt%: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less (excluding 0), S: less than or equal to 0.030% (excluding 0), and the balance Fe and other unavoidable impurities.
The reason for limiting the contents of the alloy components in the examples of the present invention will be described below. The units hereinafter are% by weight unless otherwise indicated.
The content of C is 0.60% to 0.90%.
Carbon (C) is an essential element for forming graphite particles. If the content of carbon is less than 0.60 wt%, the machinability improving effect is insufficient and the distribution of graphite particles at the end of graphitization is not uniform. Conversely, if the carbon content is too high, graphite particles are coarsened, the aspect ratio becomes large, and further the machinability, particularly the surface roughness, is lowered. Therefore, the upper limit of the carbon content may be limited to 0.90 wt%.
The content of Si is 2.0% to 2.5%.
Silicon (Si) is an essential component as a deoxidizer in the production of molten steel, and is preferably added in an amount of 2.0 wt% or more as a graphitization promoting element for destabilizing cementite in steel and precipitating carbon as graphite. However, if the content of silicon is too large, not only the effect is saturated, but also the hardness is increased by the solid solution strengthening effect, and further, the tool wear is accelerated at the time of cutting, and brittleness due to increase of non-metallic inclusions is caused, and excessive decarburization is caused at the time of hot rolling. Therefore, the upper limit of the silicon content may be limited to 2.5 wt%.
The Mn content is 0.1% to 0.6%.
Manganese (Mn) increases the strength and impact properties of the steel material, and contributes to improvement of machinability by forming MnS inclusions by bonding with sulfur in the steel, so that it is preferably added in an amount of 0.1 wt% or more. However, if the content of manganese is too large, graphitization is hindered, there is a possibility that the graphitization termination time is delayed, and the strength and hardness are increased to cause a decrease in the wear depth of the tool. Therefore, the upper limit of the manganese content may be limited to 0.6 wt%.
The content of Al is 0.01-0.05%.
Aluminum (Al) is a powerful deoxidizing element, and not only contributes to deoxidation, but also promotes graphitization. Aluminum promotes decomposition of cementite during graphitization heat treatment and also bonds with nitrogen to form AlN, thereby preventing stabilization of cementite and playing a role in promoting graphitization. In addition, since aluminum oxide formed by adding aluminum forms precipitation nuclei of graphite and effectively promotes crystallization of graphite, the addition of 0.01 wt% or more is preferable. However, if the content of aluminum is too large, not only the effect is saturated but also the heat deformability is remarkably reduced. In addition, if the amount of aluminum is too large, AlN is produced at austenite grain boundaries, and graphite with AlN as a core is unevenly distributed at the grain boundaries. Therefore, the upper limit of the aluminum content may be limited to 0.05 wt%.
The content of Ti is 0.005% to 0.02%.
Titanium (Ti) combines with nitrogen together with boron, aluminum, etc. to form nitrides such as TiN, BN, AlN, etc., which serve as nuclei for forming graphite during constant temperature heat treatment. However, BN, AlN, etc. are not uniformly precipitated in grain boundaries after austenite is formed due to low production temperature, whereas TiN is uniformly distributed in austenite grain boundaries and in grains because TiN is crystallized before austenite is completely produced due to higher production temperature than AlN or BN. Therefore, the graphite particles generated from TiN as nucleation sites are also finely and uniformly distributed. To exhibit such an effect, it is preferable to add 0.005 wt% or more, but if the content of titanium is too large, coarse carbo-nitrides are formed, carbon necessary for forming graphite is consumed, and graphitization is impaired. Therefore, the upper limit of the titanium content may be limited to 0.02 wt%.
The content of N is 0.0030% to 0.0100%.
Nitrogen (N) bonds with titanium, boron, and aluminum to form TiN, BN, AlN, and the like, and particularly nitrides such as BN, AlN, and the like are mainly formed at austenite grain boundaries. When the graphitization heat treatment is performed, since graphite is formed with these nitrides as nuclei, uneven distribution of graphite may be caused, and it is necessary to add a proper amount of nitrogen. If the amount of nitrogen added is too large, some of the nitrogen cannot be bonded to the nitride forming elements but is present in the steel in the form of solid solution nitrogen, which has the detrimental effects of improving strength and stabilizing cementite to retard graphitization. Therefore, in the present invention, the lower limit of the nitrogen content is limited to 0.0030 wt% and the upper limit is limited to 0.0100 wt% because nitrogen is consumed for forming a nitride which becomes a graphite nucleus generation site, and does not remain as solid solution nitrogen.
The content of P is less than or equal to 0.015 percent.
Phosphorus (P) is an impurity inevitably contained. Although phosphorus impairs grain boundaries to some extent to contribute to machinability, the content of phosphorus is preferably controlled to be as low as possible because of a considerable solid solution strengthening effect, resulting in an increase in ferrite hardness, a decrease in toughness and delayed fracture resistance of the steel, and promotion of surface defects. In theory, it is more advantageous to control the phosphorus content to 0 wt%, but phosphorus is inevitably contained in the manufacturing process. Therefore, it is important to control the upper limit of the phosphorus content, which is controlled to 0.015 wt% in the present invention.
The content of S is 0.030% or less.
Sulfur (S) is an impurity inevitably contained. Sulfur not only seriously hinders graphitization of carbon in steel but also segregates to grain boundaries to cause a decrease in toughness, and forms low melting point sulfides to impair hot rolling properties, and therefore, the content of sulfur is preferably controlled to be as low as possible. When the content of sulfur is too large, MnS is produced to have a machinability improving effect, but MnS elongated by rolling causes mechanical anisotropy. In the present invention, S is added within a range that does not cause mechanical anisotropy and improves machinability, to guide the production of MnS. It is more advantageous to control the sulfur content to 0 wt%, but phosphorus is inevitably contained in the manufacturing process. Therefore, it is important to control the upper limit of the phosphorus content, and in the present invention, the upper limit of the phosphorus content is controlled to 0.030% by weight.
The balance of the present invention is iron (Fe). However, the conventional manufacturing process inevitably involves mixing of unexpected impurities derived from raw materials or the surrounding environment, and thus the mixing of impurities cannot be excluded. These impurities are known to anyone skilled in the art of conventional manufacturing processes and therefore all relevant details are not repeated in this specification.
Further, according to an embodiment of the present invention, the steel material for graphite steel satisfying the foregoing alloy composition may satisfy the following formula (2).
Formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ] and [ Mn ] each represent a weight% of the element.
In the graphite steel which is a steel material after the graphitization heat treatment, since the hardness, tensile strength and ductility are affected by the addition amount of Si and Mn, in order to obtain machinability which can be satisfied in terms of chip breaking property, surface roughness and tool wear, the 3.1+169.0 x [ Si ] +127.7 x [ Mn ] value is preferably in the range of 400 to 500.
If the 3.1+ 169.0X [ Si ] + 127.7X [ Mn ] value is less than 400, the tensile strength is lowered, the surface roughness during cutting becomes poor or the chip breaking property is lowered in the characteristics of the soft material, and if the value is more than 500, the hardness value becomes high, and the degree of tool wear during cutting becomes severe.
According to an embodiment of the present invention, the steel for graphite steel satisfying the foregoing alloy composition may satisfy the following formula (1).
Formula (1): -0.01 ≤ Ti-3.43 × [ N ] 0.01 ≤
Wherein [ Ti ] and [ N ] each represent a weight% of the element.
If the [ Ti ] -3.43X [ N ] value is less than-0.01, excess nitrogen remaining after TiN formation is dissolved in the steel in a solid state to stabilize cementite, and graphitization may be delayed. Therefore, it is preferable that the value of [ Ti ] -3.43 XN ] is not less than-0.01, but if the value of [ Ti ] -3.43 XN ] is too large, Ti which is not generated as a balance of TiN may excessively exist in the steel. The balance Ti is preferably 0.01 or less in the value of [ Ti ] -3.43X [ N ] because it forms coarse carbo-nitrides, consumes the carbon forming graphite, reduces the graphite fraction, or may form coarse graphite.
The graphitization rate of the steel material for graphite steel according to the disclosed embodiment can reach more than 99% after graphitization heat treatment for 300 minutes at 730 ℃ -770 ℃.
The graphitization ratio is a ratio of the content of carbon added to the steel to the content of carbon present in the graphite state, and can be represented by the following formula (3).
Formula (3): graphitization ratio (%) (carbon content present in graphite state in steel/carbon content in steel) × 100
The graphitization of 99% or more means that all the added carbon is consumed for the formation of graphite (the amount of carbon dissolved in ferrite is not considered very small), and means that the graphite has a microstructure in which undecomposed pearlite is not present, that is, graphite particles are distributed in a ferrite matrix.
The steel material for graphite steel of the present invention described above can be produced by various methods, and the production method is not particularly limited in the present invention. For example, a steel material for graphite steel can be produced by casting a cast slab having the above composition range, performing a homogenization heat treatment at 1100 to 1300 ℃ for 5 to 10 hours, hot rolling at 1000 to 1100 ℃ and then air cooling.
Hereinafter, the graphite steel with improved machinability according to another aspect of the present invention will be described in detail.
The graphite steel according to the disclosed example has the same alloy composition and composition range as the steel for graphite steel described above, and the reason why the amount of the alloy element is limited is as described above.
That is, the graphite steel according to the disclosed embodiment may satisfy the following formula (1) or formula (2).
Formula (1): -0.01 ≤ Ti-3.43 × [ N ] 0.01 ≤
Formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ], [ Mn ], [ Ti ], [ N ] each represents a weight% of the element.
According to one embodiment of the present invention, the graphite steel for improving machinability may contain graphite particles in an area fraction of 2.0% or more in a ferrite matrix. The higher the area fraction of the graphite particles, the more improved the machinability. Therefore, the upper limit of the area fraction of the graphite particles is not particularly limited.
According to an embodiment of the present invention, the graphite particles may have an average aspect ratio of 2.0 or less. The aspect ratio of the graphite particles refers to the ratio of the longest axis to the shortest axis within one graphite particle. Thus, when the graphite particles are spheroidized, anisotropy at the time of processing is reduced, and further machinability and cold forgeability are remarkably improved.
According to an embodiment of the present invention, the graphite particles may have an average particle size of 5 μm or less. The average particle size of the graphite particles is an average equivalent circular diameter (equivalent circular diameter) of the particles detected by observing a cross section of the graphite steel, and the smaller the average particle size, the more advantageous the surface roughness is when cutting. Therefore, the lower limit of the average particle size is not particularly limited.
According to one embodiment of the present invention, the number of the graphite particles per unit area may be 1000/mm2To 5000 pieces/mm2. More specifically, the number per unit area of graphite particles having an average particle size of 3 μm or less may be 1200 particles/mm2To 3500 pieces/mm2。
As described above, when fine graphite particles are uniformly dispersed in graphite steel, the formed graphite particles reduce cutting friction, and the graphite particles become crack initiation points, so that the machinability can be remarkably improved.
According to one embodiment of the invention, the hardness of the graphite steel satisfies the range of 70HRB to 80 HRB.
The graphite steel of the present invention described above can be produced by various methods, and the production method is not particularly limited, but can be produced by the following method: for example, the steel material for graphite steel is graphitized at 730 to 770 ℃ for 600 minutes or more (constant temperature heat treatment before air cooling). The temperature range corresponds to a temperature range in the vicinity of a nose (nose) of a graphite generation curve in an isothermal transformation curve, and belongs to a temperature range in which a heat treatment time can be shortened.
This is explained in more detail below by means of preferred embodiments of the invention.
Examples
After casting ingots (Ingot) with varying contents of the respective components as shown in table 1 below, the ingots were homogenized at 1250 c for 8 hours.
Then, the steel material was hot-rolled at a finish rolling temperature of 1000 ℃ to a thickness of 27mm and air-cooled to produce a steel material for graphite steel.
[ TABLE 1 ]
Then, the steel material for graphite steel is graphitized and heat-treated at 750 ℃ for 5 hours to obtain graphite steel. However, the graphitization heat treatment temperatures of comparative examples 17 and 18 were 700 deg.C and 800 deg.C, respectively, to compare the graphitization degree based on the heat treatment temperature.
Then, the area fraction of graphite particles, the average size of graphite particles, and the average aspect ratio of graphite particles were measured with an image analyzer (image analyzer) for the steel material after the graphitization heat treatment.
The area fraction, average size and average aspect ratio of the graphite particles were determined as follows: after each sample was cut to a predetermined size, an image was taken at a magnification of 200 times with an optical microscope in a state where only polishing was performed without etching. In the image thus obtained, the difference in contrast between the matrix and the graphite phase is clearly distinguishable, and therefore, the analysis was performed using image analysis software. In addition, 15 images were taken per sample in order to improve the reliability of the analysis.
The area fraction of graphite is defined as the ratio of the area occupied by graphite to the total area observed, and the average size and aspect ratio of graphite mean the average equivalent circular diameter (equivalent circular diameter) and the ratio of the longest axis to the shortest axis in one graphite particle, respectively.
[ TABLE 2 ]
Then, in order to evaluate machinability, after machining a component, chip breaking properties, tool wear depth, and surface roughness, i.e., roughness (roughnesss) of a machined surface were measured. For this purpose, the plate-shaped steel was first graphitized at the graphitization heat treatment temperature of Table 2 for 5 hours, and then was further processed into a rod shape having a diameter of 25mm, and then was cut by a CNC automatic lathe. In the evaluation of the chip breaking property, the chip breaking was evaluated as excellent when the chips were broken at two or less rolls, as ordinary when the chips were broken at 3 to 6 rolls, and as poor when the chips were broken at 7 or more rolls. In table 2, "F", "G" and "P" represent ferrite, graphite and pearlite, respectively.
For the tool wear depth, a rod-shaped material having a diameter of 25mm was machined into 200 parts having a diameter of 15mm and a length of 200mm, and then the tool insert depths before and after machining were compared to determine the degree of wear. In this case, the cutting was carried out with the cutting oil under the conditions of a cutting speed of 100 mm/min, a moving speed of 0.1 mm/rev and a cutting depth of 1.0 mm.
[ TABLE 3 ]
Referring to tables 1 and 2, inventive examples 1 to 9 in which the compositions and the production conditions proposed in the present invention were satisfied had microstructures composed of pearlite and graphite, an area fraction of graphite was 2% or more, an average aspect ratio of graphite particles was 2.0 or less, and a density of graphite particles was 1000 particles/mm or more2. Referring to table 3, the graphite steel according to the disclosed example is excellent in chip breaking property, surface roughness, and tool life characteristics.
Referring to table 2, it can be seen that the graphitization area fraction is approximately proportional to the amount of carbon added. Thus, comparative example 10 has a graphite area fraction satisfying the range of the present invention due to the high C content, but has a relatively high aspect ratio due to the formation of coarse graphite particles. Therefore, as shown in table 3, the surface roughness of the cut surface was relatively poor.
In contrast, comparative example 11, since the C content is low, a sufficient amount of graphite is not generated, and the measured area fraction of graphite is low, not only the tool wear depth is increased, but also the chip breaking property is poor.
Comparative examples 12 to 15 are steels in which Mn and/or Si were added in the range exceeding formula (1), and hardness measurements were also outside the range of hardness values proposed in the present invention. Specifically, comparative examples 13 and 14 had hardness of 89.2 and 82.3 exceeding 80, and thus the degree of tool wear was severe.
In contrast, comparative examples 12 and 15 had hardnesses of 61.3 and 66.3 to less than 70, and thus had poor surface roughness characteristics.
Comparative examples 16 and 19 added too much N with respect to the amount of Ti added, do not satisfy formula (2), and thus failed to form TiN and remained in steel as much solid solution nitrogen, so that they were not completely graphitized within a given heat treatment time, left some pearlite, had hardness of 82.6 exceeding 80, and thus the degree of tool wear was severe.
The graphitization heat treatment temperature of comparative example 17 was 700 c lower, pearlite was not completely graphitized at the graphitization heat treatment, pearlite was observed in the microstructure, hardness was 83.1 over 80, and thus tool wear was severe.
The graphitization heat treatment temperature of comparative example 18 was high at 800 c, and after transformation into austenite, pearlite was regenerated upon cooling, and the hardness was high at 94.3, so that the tool wear was severe.
Comparative example 20 Ti added in an excessive amount with respect to the amount of N added does not satisfy formula (2), and thus coarse graphite particles are formed and the surface roughness is relatively poor.
The graphite steel according to one embodiment of the present invention forms graphite particles in a matrix to a sufficient extent, and fine graphite particles are uniformly distributed in a regular shape, so that machinability can be improved.
The exemplary embodiments of the present invention have been described above, but the present invention is not limited thereto, and those skilled in the art can make various changes and modifications within a scope not exceeding the concept and scope of the claims.
Industrial applicability
The steel material for graphite steel and graphite steel according to the embodiment of the present invention can be applied to a material for machine parts and the like.
Claims (3)
1. A steel material for graphite steel, characterized in that:
the steel material for graphite steel contains C: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less and 0 is excluded, S: 0.030% or less, excluding 0, and the balance Fe and other unavoidable impurities,
the steel material for graphite steel satisfies the following formula (1) and formula (2),
formula (1): -0.01 ≤ Ti-3.43 × [ N ] 0.01 ≤
Wherein [ Ti ] and [ N ] each represent a weight% of the element,
formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ] and [ Mn ] each represent the weight% of the element.
2. A graphite steel having improved machinability, characterized in that:
the graphite steel comprises, in weight percent, C: 0.60 to 0.90%, Si: 2.0% to 2.5%, Mn: 0.1 to 0.6%, Al: 0.01 to 0.05%, Ti: 0.005% to 0.02%, N: 0.0030% to 0.0100%, P: 0.015% or less and 0 is excluded, S: 0.030% or less, excluding 0, and the balance Fe and other unavoidable impurities,
the graphite steel satisfies the following formula (1) and formula (2),
formula (1): -0.01 ≤ Ti-3.43 × [ N ] ≦ 0.01,
wherein [ Ti ] and [ N ] each represent a weight% of the element,
formula (2): 400 is less than or equal to 3.1+169.0 x [ Si ] +127.7 x [ Mn ] < 500
Wherein [ Si ] and [ Mn ] each represent the weight% of the element,
the graphite particles are contained in the ferrite matrix by an area fraction of more than or equal to 2.0 percent,
the number of the graphite particles having an average particle size of 3 μm or less per unit area is 1200 particles/mm2To 3500 pieces/mm2，
The graphite particles have an average aspect ratio of 2.0 or less,
wherein the aspect ratio of the graphite particles means the ratio of the longest axis to the shortest axis of one graphite particle.
3. The graphite steel for improving machinability as set forth in claim 2, wherein:
the graphite steel has a hardness of 70HRB to 80 HRB.
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| KR1020170177151A KR102042063B1 (en) | 2017-12-21 | 2017-12-21 | Steel material for graphitization and graphite steel with improved machinability |
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| CN114008233B (en) * | 2020-01-22 | 2023-01-17 | 株式会社Posco | Wire rod for graphitization heat treatment, graphite steel and method for producing same |
| KR102380415B1 (en) * | 2020-04-24 | 2022-03-30 | 주식회사 삼원강재 | Free-Cutting Steel Round Bar with Improved Electomagnetic Property |
| KR102497429B1 (en) * | 2020-12-18 | 2023-02-10 | 주식회사 포스코 | Wire rod for graphitization heat treatment and graphite steel with excellent cuttability and soft magnetism |
| KR20230089718A (en) * | 2021-12-14 | 2023-06-21 | 주식회사 포스코 | Calcium-containing graphite steel with excellent cuttability and method for manufacturing the same |
| KR20230089717A (en) * | 2021-12-14 | 2023-06-21 | 주식회사 포스코 | Graphite steel wire rode, graphite steel wire, and graphite steel for tv pem nut part, methods for manufacturing and cutting the same |
| KR20230090393A (en) * | 2021-12-14 | 2023-06-22 | 주식회사 포스코 | Calcium-containing graphite steel wire rode, graphite steel wire, and graphite steel, methods for manufacturing and cutting the same |
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| JP4084462B2 (en) * | 1998-06-04 | 2008-04-30 | Ｊｆｅ条鋼株式会社 | Free-cutting hot-worked steel and its manufacturing method |
| JP3764273B2 (en) * | 1998-06-04 | 2006-04-05 | Ｊｆｅ条鋼株式会社 | Manufacturing method of hot forged steel part excellent in machinability, its part, hot rolled steel material used therefor, and manufacturing method of steel material |
| JP3255611B2 (en) * | 1998-08-19 | 2002-02-12 | エヌケーケー条鋼株式会社 | Free-cutting steel rod and wire excellent in drilling workability and method for producing the same |
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| US4061494A (en) * | 1973-12-28 | 1977-12-06 | Nippon Steel Corporation | Free-cutting graphitic steel |
| EP1045044A1 (en) * | 1998-03-04 | 2000-10-18 | Nippon Steel Corporation | Steels for cold forging and process for producing the same |
| CN101906597A (en) * | 2010-08-14 | 2010-12-08 | 武汉钢铁(集团)公司 | Environment-friendly high-performance graphitized free cutting steel |
| CN105671441A (en) * | 2014-12-09 | 2016-06-15 | Posco公司 | Steel material for graphitization and graphite steel with excellent machinability and cold forging characteristic |
| CN106191710A (en) * | 2014-12-11 | 2016-12-07 | Posco公司 | Steel and the graphitic steel of excellent in machinability for graphitization heat treatment |
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| JP6860532B2 (en) | 2021-04-14 |
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| CN109943772A (en) | 2019-06-28 |
| JP2019112711A (en) | 2019-07-11 |
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